The present invention relates to a variable current source which is capable of generating selectively currents of different magnitudes and, in particular, currents which are stable in terms of temperature and high in accuracy.
Heretofore, there has been proposed what is called a digital multi-meter as a measuring instrument which measures, for example, a voltage or resistance value and displays the measured result in the form of a digital value. Such a meter is required to be able to selectively generate predetermined various values. In this case, in order to conduct such measurements with high accuracy, it is necessary that the current values be high in accuracy and insusceptible to ambient temperature variations, that is, stable in terms of temperature. A variable current source that has been proposed, for providing various currents which are highly accurate and stable in terms of temperature, employs a reference voltage source for generating a predetermined voltage regardless of ambient temperature variations and with high accuracy and reference resistors of highly accurate resistance values and which are free from the influence of temperature variations. In addition, use is made of reference resistors of different resistance values respectively corresponding to the values of currents to be generated. As the reference resistors, winding resistors are employed. The winding resistors which are stable in terms of temperature are expensive and, especially, winding resistors of large resistance values are costly and bulky.